Current control regulator



Feb. 18, 1958 H. sTuMP 2,824,276

CURRENT CONTROL REGULATOR Filed May 4, 1955 CURRENT i GEN. E /4 r -/z l6IP 5 [4.1 22 l8 I9 2 LOAD 4 L FIG. 2

u 6 E E E E s 5 \3 VC 1p? i 3 3 =2 2 MILLIAMPERES FIG 3 HARVEY STUMPINVENTOR United Stews P t nt 2,824,276 CURRENT CONTROL REGULATOR HarveyStump, Conoga Park, CaliL, assignor to Hughes Aircraft Company, CulverCity, Calif., a corporation of Delaware Application May 4, 1955, SerialNo. 505,889 8 Claims. (Cl. 323-4) This invention relates generally toelectronic regulator circuits and, more particularly, to aself-regulating current source using a transistor as a passive controlelement.

There are many electronic circuits and systems whose satisfactoryoperation depends upon the current supply being maintained constant atall times. The operating conditions of these circuits are generally suchthat erratic and unpredictable changes in load impedance and supplyvoltages may occur.

Regulator circuits of various classes have been developed to meet thisrequirement. Among these classes are the amperite current regulator orballast tube which employs a metal filament operated in a vacuum orinert gas at an elevated temperature. This type of regulator depends onheating or cooling of the filament as current flows therethrough tochange its resistance and thus provide an error signal This introducesan inherent time lag which may be of the order of magnitude of severalseconds, depending on the construction of the ballast tube. As theballast tubes age, changes occur in their operating characteristics.They must therefore be operated, that is, aged for some time priorto'their use in a circuit in order to stabilize their characteristics.

Other types of current regulators of this class utilize thyrite, whichis a material made by General Electric Corporation and composed ofsilicon carbide with a ceramicbinding component; and thermistors, whichare made by Western Electric Corporation and composed of a mixture ofmetallic oxides with a binding component. Th'yrife has the seriouslimitation of a high temperature coetficient. If constant voltage isapplied, current through the thyrite increases 1 percent per degreecentigrade. The thermistor depends upon power dissipated within theelement to raise its temperature and lower its resistance for itsregulatory operation and thus also introduces a time-lag in regulation.

A class of regulators including vacuum tubes, particularly of thepentode type, are frequently used as constant current sources. However,to obtain the benefits inherent in a pentode, that is, a small change inplate current with changes in plate voltage, the screen grid must beconnected to a well-regulated constant voltage source.

Accordingly, it is an object of the present invention to provide acurrent regulator which automatically supplies a constant current to itsload irrespective of changes in supply voltage or the load impedance.

Another object of the present invention is to provide a self-regulatingcurrent source which reacts to correct any change in the desired outputcurrent with substantially zero lag in time.

A self-regulating. current source in accordance with the presentinvention comprises a current generator and a transistor, including anemitter, a collector, and a base. The transistor is connected betweenthe current generator and a load impedance device. The normal operatingpotentialsare applied to the current generator and the to be used forregulating purposes.

2,824,276 Patented Feb. 18, 1958 transistor. A quiescent or normaloperating point of the transistor is established by passing apredetermined current through the emitter of the transistor. Thereafter,any change in load impedance will tend to cause a change in currentflowing through the load and the transistor. This, in turn, causes achange in voltage across the transistor which is applied to the currentgenerator as an error signal. The error signal causes the currentgenerator to correct for the changed impedance by returning the currentflowing through the load to its normal operating level.

The novel features of the present invention are set forth inparticularity in the appended claims. Other and more specific objects ofthe invention will become apparent from a consideration of the followingdescription taken in connection with the accompanying drawing,illustrating embodiments of the invention in which:

Fig. 1 is a schematic circuit diagram partly in block form of thecurrent source of the present invention;

Fig. 2 is a schematic circuit diagram of the preferred embodiment of thecurrent source of the present invention;

Fig. 3 is a graph illustrating the characteristic curves of thetransistor used in the circuit of the present invention; and

Fig. 4 is a graph illustrating the characteristic curve of the vacuumtube used in the current source of the present invention.

Referring now to the drawing wherein like components are designated bythe same reference character and, more particularly, to Fig. 1, there isshown a current generator epresented by rectangle 11 including an inputelectrode 12, an output electrode 13, and a control electrode 14. Atransistor 16 is represented by its accepted schematic symbol andincludes an emitter electrode 18, a collector electrode 17, and a baseelectrode 19. Transistor 16 may be an N-P-N junction type transistor ora point contact transistor having a P-type semiconductive body asindicated by the transistor symbol. Collector 17 is connected to currentgenerator 11 to provide a path for the flow of load current. A loadimpedance device which is represented by rectangle 24 is connectedbetween emitter 18 and ground. Emitter 18 is also connected to currentgenerator 11 to provide a signal path for the control of load current.'An adjustable impedance device,'such as resistor 22, is connected toemitter 18, and a source of biasing potential, such as battery 23 hasits negative terminal connected to resistor 22 and its positive terminalto base 19. This provides a path for control current to flowthroughtransistor 16. Battery 23 is used to bias'emitter 18 in a conductingpolarity, while resistor 22 regulates.

the amount of current flowing through transistor 16from base to emitter.

In discussing the operation of the circuit of Fig. 1, reference will bemade to Fig. 3 wherein the abscissa represents collector current I inmilliamperes (ma.) and the ordinate represents collector voltage V involts. This family, of curves was taken by establishing emitter currenti varying collector voltage in steps and reading" collector current ateach step. I in quiescent condition resistor 22 is adjusted so thattransistor 16 is operating on its desired curve such as, for

example, that curve 55 of Fig. 3 represented by-emitter current I =2 ma.Assuming then that load 24 is at its optimum value and is stable, thatis, not changing at this point, a normal operating value of current isestablished. This, in turn, establishes the exact operating point oftransistor 16 as, for example, point A of curve55. If

then load 24 were to change such as to cause the current flowing throughthe load to increase, the current flowing through current generator 11and transistor 16 from emit-- ter to collector will also change. Thecurrent flowing;

3 through'transistor 16 will tend to increase toward point BI change incurrent through transistor 16 is rep resented at 51 in Fig. 3. Thisincrease in current flowing throughtransistor. 16. will causea,.variation involtage from point Alto. point .B:.a..C1'.OSS..COH6CtOl'- L7 andemitter 1.8,. theerni-tterbeing.negative: with. YESPEiCtzlZO the collector andis representedlat .52 onBig; 3, This change iHiVOltage. is applied. as an .erronsignalto.current generator 11,- the polarity. beingrsuch as totdecrease currentflowing throughthe .current generator.. Thiscauses the current to.return .to. its normaLoperating point A..

If loadimpedance, 24-0hanged; such-.as-todecreasev current,fiowingtherethroughras, forexample, along-curve 55v towards pointC,thetcurrent .flowing -fromemitter. to collector. throughtransistor. 16.will .also decrease. This, inin..turn, will cause.,a decrease.in=thevoltage drop across the:ernitter,to collectorof thetransistorasrepresentedrat 53 onFig 3. This voltageissuch as to cause. an increasein current flow through. current generator '11. This causes thecurrentzflowing through the. load to return to -its-normalpositionasrepresented at point A of Fig. 3.

It can be seen then. that there: are two paths forcurrent flow throughtransistor 16. The first path includes the emitter and base electrodes,resistor 22, and battery;23, which establishes the particular .curve ofoperation: for the transistor, such as curve 55. Thesecond-path includescollector 17, current generator 11, through ground to load-24,-andi'emitter 18.. Current flowingthrough thispathestablishesstheedesiredoperating pointon the selected characteristiccurve of transistor 16, such as: point A- on curve -55.' a

It is thus seen that transistor 16is usedas apassive circuit element.Thedynamic collector impedance, that is, the change .in. voltage acrossthe transistorwhich occurs in. responseto a: change in. currentgtherethrough, is utilized to supply the error signal for regulatoryoperation: It is {tov be:noted that aavery small change in currentthrough transistor; 16,.such as-:51,. produces. alarge-change involtage'across it,-,sucl1*:as:52, thus giving: relatively large triode31', including-a"cathode-32,: a.:control: 'gridr33, and

an'anode 34. The current generator 11 ofithisffigurexalso includes aninput electrode-12', an output electrode 13 and a-control'electrode 14'.A source-of'plate supply voltage such as :battery 35 isconnectedbetween-anode 34 and ground. A transistor41, including anemitter .43, acollector 42, and a base 44,.isshown by its acceptedschematic symbol and may be either a P N-P junction transistor or apoint contact transistor having an N-typev semiconductive bodyasindicated by the symbol. Base 44 is connected to cathode 32 whilecollector 42 isaconnected to control grid 33. A- biasingesource-ofpotential such as battery 23 has its positive terminal connected toemitter 43. An; adjustable impedance-element, .such asresistor 22, is-conn'ected: between. the negative terminal of battery 23 and base'44.Load. impedancedevice24 shown as a variable resistor 37 isconnectedbetween. collector 42 and groundi In discussing the operation othe preferred embodimentofthe present invention, asshown in Fig. 2,reference' will'b'emade'to-Fig. 3'-and also to Fig;'4 wherein theabscissa representsplate voltage E involts and the ingpl'at'e voltageandreading plate current I; A load 4. line which is determined in theusual manner is shown by line 61.

Battery 23 is poled to cause current to flow through a first pathcomprising emitter 43, base 44, resistor 22, and battery 23. Resistor 22is adjusted as in the circuit of Fig. 1 to regulate the amount .ofcurrent flowing in this path. This establishes the d'sired curve ofoperation for transistor 741,:as forzexamplefthe-icurve '55tofrFig. 3.

Assuming, as before, that load 24 is at its optimum value and-" d oesnot 'change', the current flowing through a' second path comprising-load2 4; collector42;,b'aseh44, cathode 32, anode 34, battery 35, and groundestablishes the operatinglrpointssofitransistor 41; andzofi triode 31.The operating point of triode 31 is assumed to be at the intersection ofload'line' 61With thecurve E =2 volts, point A of Fig. 4, while that oftransistor 41 is at point A of Fig. 3.

If load 2.4rnow-.changes so;asetotincrease:currentflowing-therethIough;that is, if :the value. ofvariable resistor. 37 were-to decrease;.platecurrentthroughtriode-'31-wi1'lv tendato increaseralong; load line-6150fFig. 4 irom point A toward.- point. C. Thisawill cause currentflowingthrough'. transistor; 4:1v .to 5 increase :along curve .55:toward' point This causes-.thervoltage .app'earing :across collec: tor42 -311(1:bQSGrzM {GLiDBISES as'shown. at 52 on'l igz. 3. This increasein voltage is applied across-cathode 32 andcontrol-. grid:33fof=..triode;-31;. thus-increasing the-bias :on control gridi33 as; forexample,: the-voltage-level thereon: would gQ tOWaId JEgL 4: Thisincreased biascauses: the current flowingdhnoughntriodefil: =todecrease;thus causing; it to: returnrto' itsm'ormaloperating vpointat A.

If. the value ofir resistor I 37 should: increase, currentflowing.througlr;tr-iode- 31..wouldftend to: decrease along;-

loadxlinezdl -towardrpoint-B3 This, in 'turn, willzcause the:currentaflowin'g .through:transistor'- 41-. to decrease -to wardrpoint(Lot. Fig;; 3 The decrease. in; current will again:causeraachangeainvoltage as shown; at: 53 OfliF'igg 3. Thisis appliedsacross controlugridr33 and-.-cathode-.-32,- decreasing; ther bias on controb grid; 33 andincreasing.

theacurrentziflowingzthrough triode 31: The CUFIeIlt2flDW"' ing throughtriode 31 will then return to its normal open atirigpoinhiA". I

lfi-rthe plate; supply voltagerwchangemc similar reactions 1 will occur.For-example, if plate 'voltageE variesfrom'w A; towardBt 01 2C.on:Fig.-4,.-,this.will causeaa change. in plate ,cur-rent. 1 beingthe-same -current which. flows throughload 24 andtransistor 41..Thus,.the voltage drop across transistor 41 will change.appliedracrosstthe control grid and cathode of the tube, thuscausingcurrent flowing through thetube and the load.to change backtoward its normal level.

It will be understood that 'ci'rcuit specifications .forf'the'= constantcurrent source shown in Fig.12 may vary according to the design forany-particular application; The following circuit,specifications'areincluded by' way of example only.

Although ajunctionatransistor is given as'the reference element in thecirucit-of- Fig; 2,. it is. to be understood.

that anytransiston may-be:used; It a point contact transistor isutilized; anresistancerelernent must beplaced in; the-base circuttoovercome. the negative resistancecharacteristics inherent in pointcontact transistors.

Although? a triodeeiszshown: as-theaamplifier. in Fig, 2, iti is to beunderstbod: that. any). other vacuum. :tube 11-01:

transistor may ibezused .zassa: current generator for. the:

purposes of thisinvcntion.

The .1 current :regulator .o the ,present invention may also: be.utilized.;in-.;circuitsswhere; ann-alternatingpurrent.

This change .will be waveform is to be maintained constant irrespectiveof load impedance changes, for example, where the current source is usedto control an alternating-current motor under all load conditions. Forsuch a purpose the control current flowing through emitter and base ofthe transistor reference element would be modulated with a sample of thecurrent waveform to be regulated.

There have been thus disclosed two embodiments of a self-regulatingcurrent source for reducing undesired variations in current flowingthrough the load irrespective of impedance changes in the load orchanges in supply voltage. The circuit will react substantiallyinstantaneously to either of these changes.

What is claimed is:

l. A self-regulating current source comprising: a current generatorincluding an output electrode, an input electrode, and a controlelectrode; a transistor including an emitter, a collector, and a base;means for selecting the operating curve of said transistor connectedbetween said emitter and said base; a load impedance device connectedbetween said transistor and a point of fixed potential; and saidtransistor being connected between said input and control electrodes ofsaid current generator, whereby variations of the voltage drop acrosssaid transistor are used to automatically control the current flowingthrough said current generator to maintain the current flowing throughsaid load impedance device at a predetermined level irrespective ofchanges of the impedance of said load impedance device.

2. A self-regulating current source comprising: a current generatorincluding an output electrode, an input electrode, and a controlelectrode; a transistor including an emitter, a collector, and a base; afirst conducting path including said emitter and base of said transistorfor establishing the operating curve of said transistor; a loadimpedance device connected between said transistor and said outputelectrode of said current generator; a second conducting path includingsaid transistor, said current generator, and said load impedance devicefor establishing the desired operating point on said operating curve forsaid transistor and for establishing the operating point for saidcurrent generator; and said transistor being connected between saidinput and control electrodes of said current generator, wherebyvariations of the voltage drop across said transistor are used toautomatically control the current flowing through said current generatorto maintain the current flowing through said load impedance device at apredetermined level irrespective of changes of the impedance in saidload impedance device.

3. A self-regulating current source comprising: a current generatorincluding an input electrode, an output electrode, and a controlelectrode; a transistor including an emitter, a collector, and a base; aload impedance device; a first conducting path through said transistorincluding said emitter and base and including means providing asubstantially fixed current flow therethrough for establishing theoperating curve of said transistor; and a second conducting path throughsaid transistor including said collector, said base, said currentgenerator and said impedance device having a normal desired currentflow, whereby a change in impedance of said load impedance device causesa variation of the normal desired current flowing through said secondpath which produces a change in voltage across said collector and basethat is applied across said input and control electrodes to maintain thecurrent flowing through said load impedance at the desired value.

4. The self-regulating current source defined in claim 3 wherein saidmeans included in said first conducting path includes a bias source ofpotential for biasing said emitter in a relatively conducting polarityand an adjustable impedance element for establishing the amount ofcurrent which flows in said first path.

5. The self-regulating current source defined in claim 4 wherein saidtransistor is a junction transistor of the N-P-N type and said biassource is poled to maintain said emitter negative, with respect to saidbase.

6. The self-regulating current source defined in claim 3 wherein saidcurrent generator includes a space discharge device having a cathode, ananode, and at least one control grid.

7. A self-regulating current source comprising: a space discharge devicehaving an anode, a cathode, and at least one control grid; a junctiontransistor having an emitter, a collector, and a base; a source ofoperating potential connected between said anode and a point of fixedpotential; said base being connected to said cathode, said collectorbeing connected to said control grid; a load impedance device connectedbetween said collector and said point of fixed potential; :a bias sourceof potential; and an adjustable impedance element connected in serieswith said bias source, said base, and said emitter, whereby a change involtage is produced across said collector and base in response to achange in impedance of said load, and is applied across said cathode andgrid to maintain the current flowing through said load at apredetermined value.

8. A self-regulating current source comprising: a space discharge deviceincluding an anode, a cathode, and at least one grid; a junctiontransistor of the P-N-P type having an emitter, a collector, and a base;a source of operating potential connected between said anode and a pointof fixed potential; said base being connected to said cathode, saidcollector being connected to said grid; a load impedance deviceconnected between said collector and said point of fixed potential; saidcollector being connected to said cathode, said base 'being connected tosaid grid; a load impedance device connected between said base and saidpoint of fixed potential; a bias source of potential having its positiveterminal connected to said emitter; and an adjustable resistor connectedbetween said bias source and said base, whereby a change in voltage isproduced across said collector and base in response to a change inimpedance of said load, and is applied between said cathode and grid tomaintain current flowing through said load at a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS2,576,056 Wannamaker Nov. 20, 1951 2,693,568 Chase Nov. 2, 19542,698,416 Sherr Dec. 28, 1954

